What is unusual about this case?
The patient has transitional lumbosacral anatomy, with hemisacralisation of the S1 vertebra on the right (or conversely hemilumbaristion of the left side).
Why does this matter?
Identification and clear communication of transitional anatomy is an essential part of a spinal report. If not considered, it is easy for usual landmarks to be used in perioperative plain radiography leading to operating at the incorrect level.
What level is the prior surgery at?
A defect is evident in the left laminae of the L5/S1 vertebrae (using this levelling nomenclature) - left L5/S1 hemilaminectomy. This is at the same level as the disc bulge / fibrosis.
Why has contrast been administered?
In postoperative examinations with recurrent or ipsilateral symptoms, contrast can be used for pre- and post-sequences as surgical fibrosis usually enhances where as disc material will not.
Transitional lumbosacral anatomy: the iliolumbar ligment attaches to the second last mobile segment making this vertebra L5. The S1 vertebra has a subjacent disc, but there is pseudoarthrosis of the right transverse process to the ilium.
Using this nomenclature, at L5/S1 there is left hemilaminectomy, with minor enhancing post-operative fibrosis. Residual / recurrent disc bulge at this level, with flattening and swelling of the transiting left S1 nerve root.